Neurotensin (NT) is a tridecapeptide hormone (pGlu-Leu-Tyr-Glu-Asn-Lys-Pro-Arg-Arg-Pro-Tyr-Ile-Leu-OH), originally isolated from the bovine hypothalamus [Carraway, R. and Leeman, S. E., J. Biol. Chem., 248, 6854 (1973)], has subsequently been shown to be distributed in the brain [Uhl, G. R., et al., Proc. Natl. Acad. Sci. USA, 74, 4059-4063 (1977)], gastrointestinal tract [1). Kitabgi, P., Carraway, R. and Leeman, S. E., J. Biol. Chem., 251, 7053 (1976); 2). Carraway, R., Kitabgi, P., and Leeman, S. E., J. Biol. Chem., 253, 7996 (1978); 3).Helmstadler, V., Taugner, C., Feurle, G. E. and Frossman, W. G., Histochemistry, 53, 35-41 (1977)] and pancreas [Feurle, G. E. and Niestroj, S., Pancreas, 6, 202-207 (1991) and references cited therein] of various animals including human [Mai, J. K., et al., Neuroscience, 22, 499-524 (1987)]. Although the physiological role of neurotensin has not yet been clearly understood, this endogenous peptide participates in a wide spectrum of central [1). Prange, A. J. and Nemeroff, C. B., Annal. NY Acad. Sciences, 400, 368-375 (1982); 2). Stowe, Z. N.and Nemeroff, C. B., Life Sci., 49, 987-1002; (1991); 3) Kitabgi, P., Neurochem. Int., 14, 111-119 (1989); 4). Levant and Nemeroff, C. B., Current topics in Neuroendocrinology, 8, 231-262 (1988)] and peripheral [Leeman, S. E., Aronin, N. and Ferris, C., Hormone Res., 38, 93-132 (1982)] biological functions.
Neurotensin is also known to release mast cell histamine, indicating that antagonists will be useful in the treatment of allergic and inflammatory conditions, as well. [See, Rossei, S. S. and Miller, R. J., Life Sci., 31, 509-516 (1982) and Kurose, M. and Saeki, K., Eur. J. Pharmacol., 76, 129-136 (1981).]
Neurotensin, like most other peptides, is unable to cross the blood-brain barrier (BBB). However, certain peripheral effects of neurotensin have been observed after central administration of the peptide [Prange, A. J. and Nemeroff, C. B., Annal. NY Acad. Sciences, 400, 368-391 (1982)]. The direct application of neurotensin into the brain causes hypothermia, potentiation of barbiturate induced sedation, catalepsy. antinociception, blockade of psychostimulant-induced locomotor activity and reduced food consumption. In the central nervous system (CNS), neurotensin behaves as a neurotransmitter or neuromodulator [1) Uhl, G. R. and Snyder, S. H., Eur. J. Pharmacol., 41, 89-91 (1977); 2) Uhl, G. R., Annal. NY Acad. Sciences, 400, 132-149 (1982)], and has been shown to have close anatomical and biochemical associations with the dopaminergic (DA) system [Nemeroff, C. B., et al. Annal. NY Acad. Sciences, 400, 330-344 (1982)]. Neurotensin increases the synthesis and the turnover of DA in rat brain. Acute and chronic treatment with clinically efficacious antipsychotic drugs (e.g., haloperidol, chloropromazine) have consistently demonstrated an increase in neurotensin concentrations in the nucleus accumbens and striatum while phenothiazines that are not antipsychotics did not produce this increase. Behaviorally, neurotensin, after central administration, mimics the effects of systemically administered neuroleptics. However, unlike classical neuroleptics (which primarily acts on D.sub.2 receptors), neurotensin fails to bind to dopamine receptors or inhibit cAMP accumulation following DA receptor activation. Neurotensin does not block the stereotypy induced by DA agonists. The post-mortem studies of patients with schizophrenia showed an increase in the level of neurotensin in the Brodman's area 32 of human brain [Nemeroff, C. B., et. al., Science., 221, 972-975 (1983) and references cited therein], which suggest possible roles of neurotensin in the pathophysiology of this disease. Neurotensin receptors have also been implicated in Parkinson's disease and progressive supranuclear palsy [Chinaglia, G. et al., Neuroscience, 39, 351-360 (1990)].
Of the total body neurotensin in many mammalian species, more than 80% is present in the gastrointestinal tract, especially in the distal small intestine in the endocrine like N-cells. In the gut, neurotensin stimulates pancreatic secretion [Sakamoto, T.,et al, Surgery, 96, 146-53 (1984)], inhibits gastric acid secretion and gastric emptying [Blackburn, A. M., Lancet, 1, 987-989 (1980)]. Neurotensin also stimulates the growth of small intestinal mucosa in an isolated defunctional loop of jejunum, which suggests a direct systemic effect of neurotensin in the gut. In addition, neurotensin can stimulate pancreatic exocrine secretion in mammals [Iwatsuki, K., et al., Clin. Expt. Pharmacol. Physiol., 18, 475-481 (1991) and references cited therein].
From the structural work, it is evident that the biological activity of neurotensin resides within the carboxy terminal five or six amino acid residues. The C-terminal hexapeptide NT.sup.8-13 has displayed full biological activity of the tridecapeptide. In contrast, all amino terminal partial sequences are essentially inactive [Leeman, S. E. and Carraway, R. E., Annal. NY Acad. Sciences, 400, 1-16 (1982)]. The C-terminal COOH group and two Arg residues are essential for the biological activity of NT.sup.8-13 as well as neurotensin. L-amino acids are required at positions-9, 10, 11 and 13, and only Arg.sup.8 can be replaced by D-Arg without loss of any activity. At the position-11, an aromatic amino acid is essential. Similarly, alkyl side-chains of Ile.sup.12 and Leu.sup.13 are also necessary for full biological activity [Kitabgi, P., Annal. NY Acad. Sciences, 400, 37-53 (1982)]. Most of the analogues of neurotensin examined generally behaved as agonists. However, two analogues D-Trp.sup.11 -NT and Tyr(Me).sup.11 -NT have displayed partial antagonist activity [Rioux, F. R.,et al., Eur. J. Pharmacol., 66, 373-379 (1980)].
Although there are reports of peptidic neurotensin antagonists, none are clinically useful, due to their short biological half life and limited oral bioavailability.
A European Patent Application, EP 477,049, disclosing 3-carboxamido-1,2-pyrazoles as non-peptidic neurotensin antagonists recently published.